Heretofore catheters of the needle inside type have been known and good examples of same are U.S. Pat. Nos. 3,595,230 and 3,537,456. The best known art to me at the time of filing this application are the following additional U.S. Pat. Nos. 3,906,946; 3,572,334; 3,766,915; 2,137,132 and 3,916,892. However none of these have as few moving parts of simple construction to assure a quick introduction of the catheter as soon as vein puncture is established by a positive quick thrust of the catheter into the vein.